1. Field of the Invention:
The present invention relates to a steering mechanism in motor vehicles for steering front and rear wheels in response to operation of a steering wheel.
2. Description of the Prior Art:
There are known various steering systems for motor vehicles for steering front and rear wheels in the same direction when a steering wheel is turned through a small steering angle and for steering front and rear wheels in opposite directions when the steering wheel is turned through a large steering angle. Such steering systems can improve the driving characteristics of the motor vehicle when the steering angle is relatively small while the motor vehicle is running, and also can improve the maneuverability of the motor vehicle when the steering angle is relatively large such as when the motor vehicle is turned in a garage or a parking lot. One such steering system is disclosed in Japanese Patent Laid-Open Print No. 58-97565 published on June 10, 1983.
The above Laid-Open Print discloses a vehicle steering system including a rear wheel steering mechanism having an input shaft angularly movable in response to operation of a steering wheel. An arm extends radially from the input shaft and supports on a distal end thereof a pinion in an axial direction of the input shaft, the pinion being held in meshing engagement with an internal gear fixed to a vehicle body. The pinion has an integral crank pin connected to tie rods for rear wheels.
The steering system thus employs a planetary gear mechanism comprising the pinion and the internal gear. When the pinion revolves around the center of the internal gear through a small angle, the direction of lateral movement of the crank pin due to rotation of the pinion about its own axis is opposite to the direction of lateral movement of the crank pin due to revolution of the pinion around the center of the internal gear, so that the total lateral displacement of the crank pin is small. When the angle of revolution of the pinion around the center of the internal gear becomes larger, the direction of lateral movement of the crank pin due to rotation of the pinion about its own axis is the same as the direction of lateral movement of the crank pin due to revolution of the pinion around the center of the internal gear, with the result that the overall lateral displacement of the crank pin is reversed in direction with respect to a vertical plane including an axis of the input shaft and increased. Therefore, since the maximum steering angle of the rear wheels, as they are steered in a direction opposite to that in which the front wheels are steered, can be greater than the maximum steering angle of the rear wheels as they are steered in the same direction as that in which the front wheels are steered, the driving characteristics of the vehicle are improved when the vehicle is steered through a relatively small steering angle, and a smaller radius of turning movement of the vehicle is obtained and the maneuverability thereof is improved when the vehicle is steered through a relatively large steering angle.
With the above prior-art steering system, the pinion is supported in an eccentric relation to the input shaft and the crank pin is integral with the pinion. As a consequence, the crank pin is also displaced radially off the input shaft across a large interval. The input mechanism therefore has a large moment and hence is required to have a rigidity and a strength sufficient to withstand the increased moment. For this reason, the input mechanism cannot be made more compact beyond a certain limit.